The Large Hadron Collider at CERN is a proton-proton collider where gluon-gluon interactions dominate. Many of the hadron collider's signatures for Stand Model processes and for physics beyond the Standard Model involve gluons in the initial state. It is important then that the gluon evolution be well understood. The angular decorrelation between the two highest momentum jets in an event can be used to study the dynamics of multi-jet events. The differential cross-section has been measured as a function of the opening angle in phi and the opening angle in rapidity between the two highest momentum jets in an event, using an integrated luminosity of 36 inverse pb of proton-proton collisions collected by the ATLAS detector in 2010. The resulting cross-section has been compared with predictions for several Monte Carlo generators and a NLO calculation. The sub-leading jet is required to have a transverse momentum greater than 80 GeV with the leading most jet bounded by transverse momentum regions where the lowest pT > 110 GeV and the highest pT > 800 GeV. All jets are required to be within |y|<2.8 to be considered.